In the United States, treatments for hair loss are a $3.6 billion industry with products ranging from supplements to shampoos, laser-producing helmets, and even surgery. But do any of these treatments actually work?

What Causes Hair Loss?

First, hair grows and gets longer in the anagen phase which can go on for several years. Then, during the ~10-day catagen phase, hair stops actively growing and separates from its follicle, which is what holds the hair in place beneath the skin. Finally, in the telogen phase, the follicle goes into rest mode for several months until the hair falls out. Then, the process starts anew.

The average person loses 50 to 100 hairs per day naturally due to this cycle. But if the process is interrupted at any stage—for example, if the follicle doesn’t come back out of resting mode or starts to shrink—hair loss and hair thinning can result. Interruptions to the cycle can be caused by hormones, stress, poor diet, chemical hair treatments, certain medications, and, of course, good ol' genetics.

The average person loses 50 to 100 hairs per day naturally due to this cycle.

What Is Androgenetic Alopecia?

The most common form of hair loss is androgenetic alopecia, or, in other words, male or female pattern baldness or hair loss. Androgenetic alopecia is genetic and affects an estimated 50 million men and 30 million women in the United States. Among white women in the U.S., an average of 19% are affected by female pattern hair loss, but that percentage increases with age. The prevalence is nearly doubled in Australia at 32% and much lower in Korea and China at < 6%. As of 2015, no studies had been done on the prevalence of female pattern hair loss in Brazil or Africa.

Male pattern baldness is linked to a sensitivity to the hormone dihydrotestosterone and usually manifests as a receding hairline or ring of missing hair. Female pattern baldness instead typically causes the hair to thin all over the scalp but not fall out.

Another fairly common form of hair loss is alopecia areata, which usually presents as patches of hair loss over the scalp and is autoimmune related. In autoimmune conditions, the body’s immune system attacks bodily tissues even when they are healthy. In the case of alopecia areata, the hair follicles are prevented from growing new hair.

A more temporary form of hair loss is telogen effluvium or when hair follicles get stuck in the telogen or resting phase and stop growing new hair. Telogen effluvium can occur three months after a significant medical event like childbirth, surgery, or a high fever, but can also be caused by a thyroid imbalance or iron deficiency. Certain medications like blood thinners and birth control pills are also linked to this form of hair loss.

To determine the cause of your hair loss, a doctor will typically conduct blood work to diagnose any missing nutrients or autoimmune disorders, take down your family history, study the pattern of the hair loss (in other words, is it a receding hair line or patchier in nature?) and potentially take a scalp biopsy.

Which Hair Loss Treatments Work?

The effectiveness of a hair loss treatment depends strongly on what is causing the hair loss and the list of potential causes is a long one. Not only does the treatment have to address the underlying cause of the hair loss, or alopecia, but the ability to correct different forms of hair loss itself varies. Some forms of hair loss are more easily addressed than others.

If hair loss is due to stress, nutrient loss, or lack of sleep, these causes can be temporary and hair growth can return once these triggers are addressed. Similarly, treatment for an autoimmune disorder or thyroid imbalance as the root cause of hair loss can fix the hair loss problem at the same time. The same is true for medicines or treatments that cause hair loss, for example, chemotherapy or tamoxifen for cancer treatment. In almost all cases, hair grows back in 2 to 6 months once the medication is no longer being taken. Bald patches can also occur with tight hair styles like ponytails or braids, a condition known as traction alopecia which can often be corrected by a change in hair style.